The present invention relates to a method for making it possible to evaluate certain parameters of the impulse response of the propagation channel of electromagnetic or acoustic waves, when the latter involves emitters, sensors and reflectors that are fixed or mobile, by means of a combined space/delay-distance/Doppler-kinematic ambiguities function, for the detection and the determination of the position and kinematic parameters of the emitters and of the reflectors.
It is used in many areas of electromagnetism and acoustics, in detection, transmission, location, navigation, in order to improve the knowledge of the propagation medium, consequently improve the processing of the useful signals, the engineering of the radiocommunication and broadcast radio networks, air traffic control, coastal control, etc.
It can be applied to the self-locating of a reception system implementing the invention.
It is used, for example, for emitters, reflectors and sensors that are fixed or mobile in electromagnetism and in acoustics.
The propagation, sounding, detection and location measurement systems of conventional electromagnetic or acoustic reflectors are more often than not active and generally use:                a mechanical sweep with a directional antenna (dish reflector for example) or an electronic sweep with a beam formed from an array of phase- and amplitude-weighted sensors, and        for each aiming position (or spatial cell) of the beam:                    the emission of known signals that can be continuous, pulsed or in the form of known pulse trains,            calculation of a distance/speed ambiguities function based, in the case of narrow band signals, on the correlation, with the emitted signals, of the signals observed at the antenna output and offset in time and frequency, and based in the case of wide band signals, on the correlation, with the emitted signals, of the signals observed at the antenna output that are delayed, offset in frequency, compressed in time and in frequency,                        for each distance/Doppler cell                    a threshold setting for a given false alarm probability,            a comparison of the ambiguities function with the threshold.                        
The main particular feature of this operation is the decoupling between the spatial analysis (the sweep of a beam) and the distance/speed or delay/Doppler analysis. This decoupling creates the need to systematically implement a distance/speed analysis for each beam position, whether or not there are emitters or reflectors in the beam.
Moreover, the aiming of a beam implicitly presupposes a propagation in free space (without multiple paths) and requires, for the electronic sweep, a control of the antenna pattern (model of the radiating elements and of the network, calibration of the sensor array, etc).
Also, for a given space/distance/Doppler cell, the adjustment of the threshold requires a prior estimation of the noise level based on the observation of the space/distance/Doppler cells without reflectors, which can prove difficult to implement and costly in computation terms. Furthermore, in the presence of interference, techniques for ejecting interference by spatial filtering have to be inserted in reception for each position of the swept beam, which thus becomes antijamming and robust against interference. However, since the swept beam has a certain angular width, inversely proportional to the aperture of the antenna or of the network (in terms of number of wavelengths), the rejection of the interferences for a given spatial cell can be accompanied by the rejection of the reflecting echoes present in this same cell. For this reason, techniques to increase robustness preventing the rejection of the reflectors to be measured must be incorporated in processing operations at the cost of a potential loss of performance on the rejection of the interferences and increased complexity in implementation.
The problem with measuring propagation or with electromagnetic or acoustic detection involves detecting the presence of the emitted signal s(kTe) over a certain duration 0≦k≦K−1, and estimating the channel vector hs (relating to a multiple-sensor reception and corresponding to the directing vector of the position of the reflector or of the emitter for propagation in free space), the delay loTe (assumed for simplicity to be a multiple of the sampling period, but this is by no means mandatory or limiting) and the Doppler shift Δfo=mo/KTe (the frequency resolution being 1/KTe, it is assumed for simplicity that the Doppler shift is a multiple of this resolution), from the knowledge of the emitted signal and from the observation of frequency-shifted and -translated versions of the vectors x(kTe) of the signals received on the sensor.
In the case of a conventional propagation measurement or detection application in electromagnetism or in acoustics, the conventional receivers presuppose a propagation in free space, that is to say hsejφs s and scan the space, direction by direction or vector s by vector s, with a resolution corresponding to the lobe width (generally the lobe width “at 3 dB”) of the beam formed by the network used, where hs is the vector of the impulse responses of the channels associated with the direction of the reflector, and φs and s respectively correspond to the phase and the directing vector of the emitter or of the reflector. This defines the abovementioned concept of spatial cell, commonly used by those skilled in the art. Moreover, the delay loTe is estimated with a resolution equal to 1/Be, which is nominally a function (generally proportional to) of the inverse of the equivalent band, Be, of the emitted signal, which inverse also defines the distance resolution. This defines the concept of distance cell mentioned above and commonly used by those skilled in the art. Finally, the resolution of the estimation of the Doppler shift is a function (generally proportional) of the inverse of the individual observation time, that is to say of the inverse of the duration KTe of the emitted signal. This defines the concept of Doppler cell mentioned above and commonly used by those skilled in the art.
The prior art defines different reception structures. Generally, the reception structure of an optimal detector depends on the information available a priori on the propagation channels of the signals emanating from the emitters and reflectors to be detected and on the overall noise, which comprises the thermal noise of the receivers and the potential interferences [1]. The conventional receivers used in electromagnetic [2] or acoustic [4] detection, which scan the space by electronic or mechanical sweeping of a beam and implement a spatial analysis upstream and decoupled from the distance/Doppler analysis, presuppose, generally, implicitly or explicitly, for each position of the beam and each distance/Doppler cell scanned:                a propagation in free space,        the known scanned direction,        the overall Gaussian noise, circular and unknown,        the signals emanating from emitters or from reflectors that are weak relative to the background noise,        the unknown phase of the signals emanating from the emitters or from the reflectors.        
These receivers are optimal only given these assumptions. The object of the invention is to replace the above conventional structures with a reception structure that makes it possible to overcome at least the abovementioned system drawbacks. It notably consists in effecting a coupling of the spatial analysis, and of the delay-distance/Doppler-kinematic analysis in a combined process. It implements a coupled/combined processing of the delay-distance space variables. The inventive method makes it possible notably to determine the parameters of the impulse response. These parameters are, for example, parameters relating to the spatial, temporal and frequency structure of the radioelectric field (arrival angle distributions, angular, temporal and Doppler diffusion, etc). These parameters can also be characteristics of diffusion by obstacles on the ground, in space, etc., or even kinematics parameters of the diffusers.